This invention relates to the field of voltage regulators. More particularly, this invention relates to a voltage regulator which improves power dissipation.
Some prior art RF power amplifiers use two active switching devices to generate a square wave signal. An output load network filters and transforms the signal into a sinusoidal output signal which is then transmitted. There are various problems associated with this type of power amplifier. Perhaps the largest problem with power amplifiers involves the efficiency of the amplifiers. When RF power amplifiers are used to produce high power signals, such as with transmitters, it is desired to have efficient amplifiers in order to conserve power and adequately dissipate heat. This problem is especially hard to overcome in designs utilizing CMOS devices.
Another problem relates to the use of an isolation transformer. Some prior art RF power amplifiers include a transformer connected between the pre-driver circuitry and the amplifier circuit. This presents various issues. First, a transformer is required, which uses valuable real estate on a printed circuit board (PCB) and also increases the cost of the amplifier. In addition, the transformer consumes power and generates heat.
Another problem with prior art power amplifiers involves voltage regulators. During battery charge up, the battery voltage can be much higher than the steady-state voltage. Applying this high voltage directly to a CMOS power amplifier can cause breakdown problems. Therefore, a voltage regulator may be required to provide a regulated voltage source. However, when the battery charge is high and the power amplifier is transmitting at maximum power, there is a high power dissipation in the voltage regulator which could exceed the package power rating of an integrated circuit.
When selecting the types of devices to be used in a CMOS design, such as an RF power amplifier, certain tradeoffs exist. For example, devices with smaller gate oxide thickness are faster and take up less space. However, as the gate oxide thickness gets smaller, the breakdown voltage of the device also gets smaller. Therefore, when selecting devices in a CMOS design a problem develops in getting a suitable breakdown voltage as well as a suitable speed for a device.
Another problem with prior art power amplifiers relates to amplifiers using a push-pull architecture. A push-pull architecture requires very low inductance and resistance in the ground and signal connections of the integrated circuit to the PCB. In a typical wire bond package, the bond wire inductance can be large enough to cause problems. In addition, the resistance of on-chip wiring using thin on-chip conductors can cause significant losses.
A voltage regulator of the present invention provides a regulated voltage to a device residing on an integrated circuit, the voltage regulator including a first regulator coupled between a voltage source and the power amplifier, the first regulator residing on the integrated circuit, a second regulator coupled between the voltage source and the power amplifier, the second regulator residing on the integrated circuit, and an external resistor coupled between the second regulator and the voltage source for dissipating power outside the integrated circuit.
Another embodiment of the invention provides a voltage regulator for providing a regulated voltage to an integrated circuit on which the voltage regulator resides, the voltage regulator comprising a regulator circuit coupled to a voltage source, and an external resistor coupled to the regulator circuit for dissipating power outside the integrated circuit.
Another embodiment of the invention provides a method of providing a regulated a voltage from a voltage source comprising the steps of providing a first regulator circuit coupled to the voltage source, providing a second regulator circuit coupled to the voltage source, and connecting a resistance between the second regulator circuit and the voltage source.
Other objects, features, and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows below.